Air-guiding photonic bandgap fibers are developed into application in various areas.Microbending loss properties of fiber play an important role in practical application including optical communications and optical fiber senors.Microbending losses in air-guiding photonic bandgap (PBG) fiber are investigated experimentally.Transmission spectra of PBG fiber subjected to microbending under different pressure and conditions are measured.Various factors which affect the microbending loss,including wavelength,pressure,bending period,and diameter,are analyzed.An analysis of the losses associated with surface modes and mode coupling is presented.The results show that,as the existing of surface modes,spectral losses of PBG fiber increase with the wavelength in the band of 1520-1620 nm.Moreover,within the critical period,transmission loss increases with the microbending period.Additionally,as the diameter of the microbending increases,the fiber is found to be more sensitive to the bending loss.